The invention relates to an uninterruptible power supply with passing neutral.
In most uninterruptible power supplies with common neutral between the input and output, a first rectifier stage supplies, from the mains power system, a DC voltage on a DC bus, to the terminals of two serially-connected capacitors whose mid-point is connected to the common neutral. The output AC voltage of the power supply is obtained between the common neutral and the output of a half-bridge DC-AC converter connected to the terminals of the DC bus. A battery is connected to the DC bus via a DC-DC converter.
In the document GB-A-2,111,326, the rectifier stage comprises two diodes forming a doubler and the DC-DC converter which interfaces the battery bank comprises an H.F. step-up transformer. The use of single rectification does not enable an AC voltage of sufficient amplitude to be guaranteed on output whatever the tolerances of the input power system.
The document U.S. Pat. No. 5,126,585 describes an uninterruptible power supply in which the rectifier stage comprises a reversible rectifier and the DC-DC converter which interfaces the battery bank by a single step-up chopper.
It has also been proposed to connect a twin step-up chopper between a first DC bus, connected both to the output of a rectifier and to the output of a DC-DC converter, with an H.F. transformer having a secondary with mid-point and whose primary is connected to the battery, and a second DC bus connected to the input of the DC-AC converter. The common neutral is then connected to the mid-point of the transformer and to the mid-point of two capacitors connected in series both upline and downline from the twin step-up chopper. In this power supply, as in the previous one, a DC-DC converter is dedicated to the battery bank.